This invention relates to an ink jet ink printing method using an ink jet ink composition containing a quaternized nitrogen heterocyclic azo dye.
Ink jet printing is a non-impact method for producing images by the deposition of ink droplets in a pixel-by-pixel manner to an image-recording element in response to digital signals. There are various methods which may be utilized to control the deposition of ink droplets on the image-recording element to yield the desired image. In one process, known as continuous ink jet, a continuous stream of droplets is charged and deflected in an imagewise manner onto the surface of the image-recording element, while unimaged droplets are caught and returned to an ink sump. In another process, known as drop-on-demand ink jet, individual ink droplets are projected as needed onto the image-recording element to form- the desired image. Common methods of controlling the projection of ink droplets in drop-on-demand printing include piezoelectric transducers and thermal bubble formation. Ink jet printers have found broad applications across markets ranging from industrial labeling to short run printing to desktop document and pictorial imaging.
The inks used in the various ink jet printers can be classified as either dye-based or pigment-based. A dye is a colorant which is dissolved in the carrier medium. A pigment is a colorant that is insoluble in the carrier medium, but is dispersed or suspended in the form of small particles, often stabilized against flocculation and settling by the use of dispersing agents. The carrier medium can be a liquid or a solid at room temperature in both cases. Commonly used carrier media include water, mixtures of water and organic co-solvents and high boiling organic solvents, such as hydrocarbons, esters, ketones, etc.
The choice of a colorant in ink jet systems is critical to image quality. For colors such as cyan, magenta, yellow, green, orange, etc., the peak wavelength (xcex-max), the width of the absorption curve and the absence of secondary absorptions are important. The colorant should also have a high degree of light fastness after printing onto the ink-receiving element. For aqueous dye-based inks, the dye needs to be sufficiently soluble in water to prepare a solution that is capable of producing adequate density on the receiving element and stable for extended periods of storage without precipitation. High quality ink jet printing with dye-based inks requires dyes which will provide both bright hue and good light stability. It is difficult to find dyes which meet all of these requirements.
Another group of dyes are basic or cationic dyes which were developed mainly for the dyeing of synthetic textile fibers such as acrylics and acid-modified polyesters. These dyes are positively charged, due to either the incorporation of pendant, positively-charged substituent groups, such as tetraalkylammonium, or by virtue of the basic chromophore comprising a delocalized cationic system such as a cyanine, azacyanine or azo (diazacyanine).
U.S. Pat. No. 5,560,996 discloses a variety of cationic dyes, including cationic azo dyes such as Basic Red 46 and other cationic magenta dyes such as Basic Reds 12, 14 and 15 for use in an ink jet ink. As will be shown below, these dyes have poor light stability.
It is an object of this invention to provide an ink jet printing method using cationic dyes suitable for use in aqueous inks for ink jet printing that will provide bright, light stable images.
This and other objects are achieved in accordance with this invention which relates to an ink jet printing method, comprising the steps of:
A) providing an ink jet printer that is responsive to digital data signals;
B) loading the printer with ink-receptive elements comprising a support having thereon a porous ink-receptive layer;
C) loading the printer with an ink jet ink composition comprising water, a humectant, and a delocalized cationic azo dye derived from the quatemization of a nitrogen heterocyclic azo dye having the following formula: 
xe2x80x83wherein:
Z represents the atoms necessary to complete a nitrogen-containing heterocyclic ring containing 2 or 3 nitrogen atoms and the balance carbon atoms;
R1 and R2 each independently represents hydrogen or a substituted or unsubstituted alkyl group of 1 to about 6 carbon atoms;
R4, R5 and R6 each independently represents the same substituents as R1 and R2, halogen, cyano, substituted or unsubstituted alkoxy, acyl, benzoyl or alkoxycarbonyl; with the proviso that at least one of R4, R5 and R6 represents a substituted or unsubstituted alkyl group of 1 to about 6 carbon atoms attached to a nitrogen atom;
R3 represents the same groups as R4, R5 and R6; hydroxy; a polyoxyalkylene group of 2-20 alkylene oxide residues; carboxy or sulfo or phospho ester; carbamoyl; substituted or unsubstituted alkyl-, aryl-aralkyl-, diaryl- or dialkyl-carbamoyl of 1 to about 20 carbon atoms; sulfamoyl; substituted or unsubstituted alkyl-, aryl-, aralkyl-, diaryl- or dialkyl-sulfamoyl of 1 to about 20 carbon atoms; acylamino; sulfonylamino; amino; a substituted or unsubstituted alkyl-, aryl-, aralkyl-, diaryl- or dialkylamino-of 1 to about 20 carbon atoms; or a quaternary ammonium or phosphonium group; or may be combined with R2 to form a carbocyclic or heterocyclic 5 or 6 membered ring;
n is 1 except when Z represents the atoms necessary to complete a nitrogen-containing heterocyclic ring containing 3 nitrogen atoms, in which case n is 0; and
X represents a counterion, such as citrate, gluconate or lactate;
xe2x80x83with the proviso that when Z represents the atoms necessary to complete a nitrogen-containing heterocyclic ring of 3 nitrogen atoms, then R3 is combined with R2 to form a carbocyclic or heterocyclic 5 or 6 membered ring; and
D) printing on an ink-receptive substrate using the ink jet ink in response to the digital data signals.
It has been found that use of the above dyes provides excellent hue characteristics and light stability.
Quaternized nitrogen heterocyclic-azo dyes are not new. They have been used for dyeing fabrics, particularly polyacrylonitrile fabrics. Typical examples are quaternized pyrazole-azo, imidazole-azo, triazole-azo dyes. Their use been described for this purpose in xe2x80x9cChemistry and Application of Dyesxe2x80x9d ed. Waring and G. Hallas, (Plenum Press), p184. A typical preparation of of this type is also described in the above reference (p197).
Examples of dyes which can be used in the invention are as follows:
In a preferred embodiment of the invention, R1 in the above formula represents hydrogen. In another preferred embodiment, R2 represents C4H9. In still another preferred embodiment, R2 and R3 are taken together and represent a tetrahydroquinoline ring. In yet another preferred embodiment, R4 represents CN or CON(C2H4OH)2. In still another preferred embodiment, R5 and R6 each represents CH3.
In general, the above dyes comprise from about 0.2 to about 5%, preferably from about 0.5 to 3%, by weight of the ink jet composition.
The water solubility of cationic dyes is significantly affected by the nature of the counterion X. The counterion preferred for solubility is often not readily incorporated during the synthesis. Ion exchange via ion exchange resins or dialysis/ultrafiltration or deprotonation and reprotonation with the desired acid counterion, is often necessary to produce dyes having the preferred salt for high water solubility.
In addition to the colorant, other ingredients are also commonly added to ink jet inks. Water miscible organic solvents humectants and/or co-solvents may be added to aqueous inks to help prevent the ink from drying out or crusting in the orifices of the printhead or to help the ink penetrate the receiving substrate, especially when the substrate is a highly sized paper. Examples of such solvents include glycols and derivatives thereof, including propylene glycol, polypropylene glycol, ethylene glycol, polyethylene glycol, diethylene glycol, glycerol, thiodiethanol, tetraethylene glycol (and mixtures and derivatives thereof), low molecular weight alcohols such as ethanol and isopropanol and amides such as N-methylpyrrolidone.
A humectant is employed in the ink jet composition employed in the invention to help prevent the ink from drying out or crusting in the orifices of the printhead. Examples of humectants which can be used include polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, tetraethylene glycol, polyethylene glycol, glycerol, 2-methyl-2,4-pentanediol 1,2,6-hexanetriol and thioglycol; lower alkyl mono- or di-ethers derived from alkylene glycols, such as ethylene glycol mono-methyl or mono-ethyl ether, diethylene glycol mono-methyl or mono-ethyl ether, propylene glycol mono-methyl or mono-ethyl ether, triethylene glycol mono-methyl or mono-ethyl ether, diethylene glycol di-methyl or di-ethyl ether, and diethylene glycol monobutylether; nitrogen-containing cyclic compounds, such as pyrrolidone, N-methyl-2-pyrrolidone, and 1,3-dimethyl-2-imidazolidinone; and sulfur-containing compounds such as dimethyl sulfoxide and tetramethylene sulfone. A preferred humectant for the composition employed in the invention is diethylene glycol, glycerol, or diethylene glycol monobutylether.
Water-miscible organic solvents may also be added to the aqueous ink employed in the invention to help the ink penetrate the receiving substrate, especially when the substrate is a highly sized paper. Examples of such solvents include alcohols, such as methyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, t-butyl alcohol, iso-butyl alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol; ketones or ketoalcohols such as acetone, methyl ethyl ketone and diacetone alcohol; ethers, such as tetrahydrofuran and dioxane; and esters, such as, ethyl lactate, ethylene carbonate and propylene carbonate.
Surfactants may be added to adjust the surface tension of the ink to an appropriate level. The surfactants may be anionic, cationic, amphoteric or nonionic.
A biocide may be added to the composition employed in the invention to suppress the growth of micro-organisms such as molds, fungi, etc. in aqueous inks. A preferred biocide for the ink composition of the present invention is Proxelg(copyright) GXL (Zeneca Specialties Co.) at a final concentration of 0.0001-0.5 wt. %.
The pH of the aqueous ink compositions employed in the invention may be adjusted by the addition of organic or inorganic acids or bases. Useful inks may have a preferred pH of from about 2 to 10, depending upon the type of dye being used. Typical inorganic acids include hydrochloric, phosphoric and sulfuric acids. Typical organic acids include methanesulfonic, acetic and lactic acids. Typical inorganic bases include alkali metal hydroxides and carbonates. Typical organic bases include ammonia, triethanolamine and tetramethylethlenediamine.
A typical ink composition employed in the invention may comprise, for example, the following substituents by weight: colorant (0.05-5%), water (20-95%), a humectant (5-70%), water miscible co-solvents (2-20%), surfactant (0.1-10%), biocide (0.05-5%) and pH control agents (0.1-10%).
Additional additives which may optionally be present in the ink jet ink composition employed in the invention include thickeners, conductivity enhancing agents, anti-kogation agents, drying agents, and defoamers.
The ink jet inks employed in this invention may be employed in ink jet printing wherein liquid ink drops are applied in a controlled fashion to an ink receptive layer substrate, by ejecting ink droplets from a plurality of nozzles or orifices of the print head of an ink jet printer.
Ink-receptive substrates useful in ink jet printing are well known to those skilled in the art. Representative examples of such substrates are disclosed in U.S. Pat. Nos. 5,605,750; 5,723,211; and 5,789,070 and EP 813 978 A1, the disclosures of which are hereby incorporated by reference.
The following example illustrates the utility of the present invention.